Renin-angiotensin system genes in kidney development

Phylogeny and ontogeny of the renin-angiotensin system: Current view and perspectives

The renin-angiotensin system (RAS) evolved early among vertebrates and remains functioning throughout the vertebrate phylogeny and has adapted to various environments. The RAS is crucial for the regulation of blood pressure, fluid-electrolyte balance and tissue homeostasis. The RAS is also expressed during early ontogeny in renal and extra-renal tissues, and exerts unique vascular growth and differentiation functions. In this brief review, we describe advances from molecular-genetic and whole animal approaches and discuss similarities and unique aspects of the RAS in the context of embryonic development and vertebrates' phylogeny.

Ontogeny of renin gene expression in the chicken, Gallus gallus

Renin or a renin-like enzyme evolved in ancestral vertebrates and is conserved along the vertebrate phylogeny. The ontogenic development of renin, however, is not well understood in nonmammalian vertebrates. We aimed to determine the expression patterns and relative abundance of renin mRNA in pre- and postnatal chickens (Gallus gallus, White Leghorn breed). Embryonic day 13 (E13) embryos show renal tubules, undifferentiated mesenchymal structures, and a small number of developing glomeruli. Maturing glomeruli are seen in post-hatch day 4 (D4) and day 30 (D30) kidneys, indicating that nephrogenic activity still exists in kidneys of 4-week-old chickens. In E13 embryos, renin mRNA measured by quantitative polymerase chain reaction in the adrenal glands is equivalent to the expression in the kidneys, whereas in post-hatch D4 and D30 maturing chicks, renal renin expressions increased 2-fold and 11-fold, respectively. In contrast, relative renin expression in the adrenals became lower than in the kidneys. Furthermore, renin expression is clearly visible by in situ hybridization in the juxtaglomerular (JG) area in D4 and D30 chicks, but not in E13 embryos. The results suggest that in chickens, renin evolved in both renal and extrarenal organs at an early stage of ontogeny and, with maturation, became localized to the JG area. Clear JG structures are not morphologically detectable in E13 embryos, but are visible in 30-day-old chicks, supporting this concept.

Enhanced angiotensinogen expression in neonates during kidney development

BACKGROUND

We recently demonstrated that preterm neonates have higher urinary angiotensinogen (AGT) levels than full-term neonates. Here, we tested the hypothesis that enhanced neonatal AGT expression is associated with intrarenal renin-angiotensin system (RAS) status during kidney development.

METHODS

We prospectively recruited neonates born at our hospital and healthy children with minor glomerular abnormalities between April 2013 and March 2017. We measured neonatal plasma and urinary AGT levels at birth and 1 year later and assessed renal AGT expression in kidney tissues from neonates and healthy children using immunohistochemical (IHC) analysis.

RESULTS

Fifty-four neonates and eight children were enrolled. Although there were no changes in plasma AGT levels, urinary AGT levels were significantly decreased 1 year after birth. Urinary AGT levels at birth were inversely correlated with gestational age, and urinary AGT levels at birth and 1 year later were inversely correlated with estimated glomerular filtration rate 1 year after birth. IHC analysis showed that renal AGT expression in neonates was higher than that in healthy children and inversely correlated with gestational age.

CONCLUSIONS

Enhanced AGT expression and urinary AGT excretion may reflect intrarenal RAS activation associated with kidney development in utero.

Perinatal Taurine Imbalance Followed by High Sugar Intake Alters the Effects of Estrogen on Renal Excretory Function in Adult Female Rats

This study tests the hypothesis that perinatal taurine imbalance impairs renal function in adult female rats via alterations in estrogen activity. Female Sprague-Dawley rats were fed normal rat chow and water containing 3% beta-alanine (TD), 3% taurine (TS) or water alone (C) from conception until weaning. Then, female offspring received normal rat chow and water with (CG, TDG, TSG) or without (CW, TDW, TSW) 5% glucose. At 7-8 weeks of age, renal function at rest and after acute saline load was tested in conscious, restrained female rats treated with non-selective estrogen receptor blocker tamoxifen for a week. Compared to control, TD or TS did not affect mean arterial pressure (MAP). Tamoxifen significantly increased resting MAP only in TDG compared to TDW groups. Although renal blood flow did not significantly differ among the groups, renal vascular resistance increased in TSG compared to CW, CG, and TSW groups. Glomerular filtration rate and water and sodium excretion were not significantly different among the groups. Compared to CW, saline load significantly depressed fractional water excretion in CG, TDW, TDG, and TSW, and fractional sodium excretion in CG, TDW, TDG, TSW, and the TSG groups. Potassium excretion was not significantly different among the corresponding groups. Fractional potassium excretion significantly increased in TDW compared to CG and in TSG compared to CG and TSW groups. These differences were abolished by tamoxifen treatment. These data indicate that in adult female rats, perinatal taurine imbalance, particularly followed by high sugar intake, alters renal function via an estrogenic mechanism.

Renin-angiotensin system in vertebrates: phylogenetic view of structure and function

Renin substrate, biological renin activity, and/or renin-secreting cells in kidneys evolved at an early stage of vertebrate phylogeny. Angiotensin (Ang) I and II molecules have been identified biochemically in representative species of all vertebrate classes, although variation occurs in amino acids at positions 1, 5, and 9 of Ang I. Variations have also evolved in amino acid positions 3 and 4 in some cartilaginous fish. Angiotensin receptors, AT₁ and AT₂ homologues, have been identified molecularly or characterized pharmacologically in nonmammalian vertebrates. Also, various forms of angiotensins that bypass the traditional renin-angiotensin system (RAS) cascades or those from large peptide substrates, particularly in tissues, are present. Nonetheless, the phylogenetically important functions of RAS are to maintain blood pressure/blood volume homeostasis and ion-fluid balance via the kidney and central mechanisms. Stimulation of cell growth and vascularization, possibly via paracrine action of angiotensins, and the molecular biology of RAS and its receptors have been intensive research foci. This review provides an overview of: (1) the phylogenetic appearance, structure, and biochemistry of the RAS cascade; (2) the properties of angiotensin receptors from comparative viewpoints; and (3) the functions and regulation of the RAS in nonmammalian vertebrates. Discussions focus on the most fundamental functions of the RAS that have been conserved throughout phylogenetic advancement, as well as on their physiological implications and significance. Examining the biological history of RAS will help us analyze the complex RAS systems of mammals. Furthermore, suitable models for answering specific questions are often found in more primitive animals.

Identity of the renin cell is mediated by cAMP and chromatin remodeling: an in vitro model for studying cell recruitment and plasticity

The renin-angiotensin system (RAS) regulates blood pressure and fluid-electrolyte homeostasis. A key step in the RAS cascade is the regulation of renin synthesis and release by the kidney. We and others have shown that a major mechanism to control renin availability is the regulation of the number of cells capable of making renin. The kidney possesses a pool of cells, mainly in its vasculature but also in the glomeruli, capable of switching from smooth muscle to endocrine renin-producing cells when homeostasis is threatened. The molecular mechanisms governing the ability of these cells to turn the renin phenotype on and off have been very difficult to study in vivo. We, therefore, developed an in vitro model in which cells of the renin lineage are labeled with cyan fluorescent protein and cells actively making renin mRNA are labeled with yellow fluorescent protein. The model allowed us to determine that it is possible to culture cells of the renin lineage for numerous passages and that the memory to express the renin gene is maintained in culture and can be reenacted by cAMP and chromatin remodeling (histone H4 acetylation) at the cAMP-responsive element in the renin gene.

The human renin kidney enhancer is required to maintain base-line renin expression but is dispensable for tissue-specific, cell-specific, and regulated expression

Renin is the rate-limiting enzyme in the renin-angiotensin system and thus dictates the level of the pressor hormone angiotensin-II. The classical site of renin expression and secretion is the renal juxtaglomerular cell, where its expression is tightly regulated by physiological cues. An evolutionarily conserved transcriptional enhancer located 11 kb upstream of the human RENIN gene has been reported to markedly enhance transcription in renin expressing cells in vitro. However, its importance in vivo remains unclear. We tested whether this enhancer is required for appropriate tissue- and cell-specific expression, or for physiological regulation of the human RENIN gene. To accomplish this, we used a retrofitting technique employing homologous recombination in bacteria to delete the enhancer from a 160-kb P1-artificial chromosome containing human RENIN, two upstream genes and one downstream gene, and then generated two lines of transgenic mice. We previously showed that human renin expression in transgenic mice containing the wild type construct is tightly regulated as is expression of the linked genes. Deletion of the enhancer had no effect on tissue-specific expression of human RENIN, but using the downstream gene as an internal control, found that human RENIN mRNA levels were 3-10-fold decreased compared with constructs containing the enhancer. Despite this decrease in expression, renin protein remained localized to renal juxtaglomerular cells and was appropriately regulated by cues that either increase or decrease expression of renin. Our results suggest that sequences other than the enhancer may be necessary for tissue-specific, cell-specific, and regulated expression of human RENIN.

Further insights into the role of angiotensin II in kidney development

Over the past decade, compelling studies have highlighted the fundamental role of the renin-angiotensin system (RAS) in renal development and long-term control of renal function and arterial pressure. The present review provides an update of the understanding of how the RAS controls nephrogenesis and nephrovascular development. In addition, the investigations linking the perinatal development of RAS inhibition-induced renal dysmorphology and establishment of adult blood pressure are discussed.

Quantitative study of the comma-shaped body, S-shaped body and vascularized glomerulus in the second and third human gestational trimesters

BACKGROUND

The rat developing metanephros has been quantified, but not the human developing kidney.

AIMS

To contribute to the knowledge of the human developing kidney by studying the relative growth of the glomerular structures subtypes in the last two gestational trimesters.

MATERIAL AND METHODS

The glomerular compartment of 21 human fetal left kidneys was studied. A stereological study determined the volume density (V(V)), the surface density (S(V)), and the numerical density in the plane (N(A)) of the developing glomeruli in the stages of comma-shaped body (C), S-shaped body (S), and vascularized glomerulus. Growth curves used log-transformed data and the allometric model.

RESULTS

Reduction of both C and S bodies, and, consequently, a relative growth of the vascularized glomerulus from the second to the third trimesters. The differences between ages were not significant to the S body V(V) and S(V), but there was a significant N(A) reduction from the second to the third trimesters. An age-related reduction of the C body and an intense growth of the vascularized glomerulus were observed in this period. The allometric coefficient b was negative in both C and S bodies and positive in the vascularized glomerulus in the last two gestational trimesters.

CONCLUSION

The growth equations and the observed tendencies of these glomerular subtypes in human fetal life could be useful to assess the kidney maturity through invasive or noninvasive investigative methods in the future.

Regulation of the renal proximal tubule second sodium pump by angiotensins

For several years it was believed that angiotensin II (Ang II) alone mediated the effects of the renin-angiotensin system. However, it has been observed that other peptides of this system, such as angiotensin-(1-7) (Ang-(1-7)), present biological activity. The effect of Ang II and Ang-(1-7) on renal sodium excretion has been associated, at least in part, with modulation of proximal tubule sodium reabsorption. In the present review, we discuss the evidence for the involvement of Na+-ATPase, called the second sodium pump, as a target for the actions of these compounds in the regulation of proximal tubule sodium reabsorption.

IGF-I treatment attenuates renal abnormalities induced by neonatal ACE inhibition

An intact renin-angiotensin system (RAS) during nephrogenesis is essential for normal renal development. We have shown previously that neonatal inhibition of the RAS, either with ANG II type 1-receptor blockade or angiotensin-converting enzyme (ACE) inhibition, induces irreversible renal abnormalities. The aim of the present study was to investigate whether an interrupted RAS can be compensated for by exogenous administration of another important renal growth-promoting factor, the insulin-like growth factor-I (IGF-I). Rats were treated daily with either the ACE inhibitor enalapril (10 mg/kg), recombinant human IGF-I (3 mg/kg), or the combination enalapril + IGF-I from perinatal day 3 to 13. Urinary concentrating ability, renal function, and renal morphology were assessed at adult age. The gene expression and localization of IGF-I, its receptor, and the growth hormone receptor (GHR) were investigated during ongoing ACE inhibition. The present study demonstrates normalized renal function and histology in enalapril + IGF-I-treated animals. Ongoing ACE inhibition suppressed the medullary IGF-I mRNA expression and altered the local distribution of both IGF-I and GHR. Thus the present study provides evidence for an interaction between the RAS and GH/IGF-I axis in renal development.